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Metal heat

  1. Feb 24, 2008 #1
    Hi,

    I understand what make metal a conductor of electricity, but what allows it to conduct heat? Is it that it does not absorb heat because it's electrons are easily liberated?
     
  2. jcsd
  3. Feb 24, 2008 #2
    What do you mean by " it does not absorb heat"? Metals do absorb heat and even faster than those can not conduct heat well. The reason that metals conduct heat well is the liberated electrons.
     
  4. Feb 25, 2008 #3

    ZapperZ

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    Remember what "heat" is in thermodynamics. It is nothing more than "energy of vibration".

    In metals, there are 2 different ways for them to absorb heat: via lattice vibration, and via the free electron gas. Most of the heat is absorbed by the lattice vibration because the free electron gas has a very low specific heat. However, the ability of metal to conduct heat very well and transfer it very efficiently throughout its volume better than an insulator is due to these very mobile conduction electrons. So these electrons can carry the heat energy faster throughout the metal.

    So how come an insulator doesn't? Other than the lack of these free conduction electrons, insulator also tends to have an amorphous crystal structure (unlike metals that tend to be crystalline), or highly polycrystalline (not large single-crystals like metals). When you have something amorphous or polycrystalline, the vibrations in one part of the material do not transfer well to other parts. So the heat transfer is very slow in such material.

    Zz.
     
  5. Feb 25, 2008 #4
    About that, why diamond has a very high heat conduction coefficient? I assume it has a very "efficient" way of propagating phonons, and if this is true, why?
     
  6. Feb 25, 2008 #5

    Mapes

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    ...why diamond has a very high heat conduction coefficient? I assume it has a very "efficient" way of propagating phonons, and if this is true, why?

    The covalent bonds in diamond are strong. The crystal structure consists of two interpenetrating face-centered-cubic lattices (this is called a diamond cubic structure), which means that each carbon atom has tetragonal coordination. The result is a 3-D arrangement of bonds that is strong in all directions (in contrast to graphite, which is characterized by a 2-D molecular arrangement).

    Diamond can be thought of as a single giant molecule that is held together tightly. Its strong bonds and particular crystal structure lead to high stiffness, low thermal expansion, high sublimation point, brittle fracture, and finally, high thermal conductivity.
     
  7. Feb 25, 2008 #6
    Corundum (aluminum oxide), e.g., has very strong bonds too (yes, not so strong, but however very strong) but it's 30 times less conductive than diamond and at least 6 times less conductive than aluminum. Why? Your explanation doesn't seem so good.
     
    Last edited: Feb 25, 2008
  8. Mar 22, 2008 #7

    Mapes

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    OK, let's hear your explanation. :smile: To be fair, it should explain diamond's high thermal conductivity, plus an experimental fact of my choosing, to be disclosed after you reply.
     
  9. Mar 24, 2008 #8
    Photons and heat are different concepts.
     
  10. Mar 24, 2008 #9

    dst

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    Phonons and heat are very closely linked.
     
  11. Mar 24, 2008 #10
    As are heat and temperature. It's a bit inaccurate to say an object possesses "heat," because heat is one way of transferring energy (the other being work). If a metal is "hot," it just has a high average molecular kinetic energy which translates into a high temperature in human tactile terms.
     
  12. Mar 25, 2008 #11
    That's perfect!
    One little note, anyway: if I had that answer, I wouldn't have asked the question in my post N. 4. :smile:
     
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